The present invention relates to a process for the manufacture of cooking vessels, in particular pots and/or pans and the like provided with a bottom reinforced with a plate member made of a hard material associated thereto, and also a vessel as above defined, obtained according to such process.
In particular, said process refers to cooking vessels shaped starting from a relatively soft metallic flat member, e.g. made of aluminium, and comprising a bottom portion reinforced with said plate member which is formed in a metallic material of relatively high hardness, e.g., steel-based, possibly having properties making it heatable with a magnetically induced current.
The processes and the related vessels of the above specified type are known in the art. For instance, the French Patent Application No. 91/03695 and the European Patent No. 0,604,617, in the name of SEB S.A., describe a step in which the plate member and the flat member are reciprocally connected with a hot press-stamping.
In this step, the soft material of the flat member is heated and softened. Then, the plate member, that is provided with holes and/or fissures, is press-stamped, e.g. with a hammer or the like, in such a way that the steel plate member is embedded into the aluminium flat member while the latter, due to the induced pressure, penetrates inside said holes.
Such process is disadvantageous due to several reasons, among which the necessity of a step of heating the aluminium, with the entailed consumption of energy and time, and the need to protect the aluminium itself from oxidation processes.
In the European Patent No 0.509.860, a method is described for embedding a holed steel plate in an aluminium layer apt to be manufactured in order to obtain a cooking vessel. According to such method, the embedding is carried out with an energetic step of cold press-stamping, in which the malleability of the aluminium is exploited that is forced to penetrate inside the holes and the fissures of the plate.
Such step, preceding the drawing of the aluminium layer, is a remarkable trauma for the materials and requires the use of high pressures for the cold press-stamping.
In the Swiss Patent No. 227,769 a further method is described for coupling, wherein a spiral-shaped reinforcing member is irreversibly forced inside a groove, of similar shape, formed on a face of the flat member in a soft material.
This method, besides entailing an additional step of hot-or cold forming of said groove, does not allow an application of a real plate member.
In the Italian Patent Application No. RM91A000355 a further method is described, according to which a metallic plate of ferritic steel is fixed to the bottom of a pot by forcing and crimping the edge of the plate inside a peripheral groove surrounding the bottom of the pot already shaped.
This method, although performing an effective coupling without overly traumatising the material, does not provide a suitable reinforcement.
The technical problem underlying the present invention is that of providing a process for the manufacture of cooking vessels allowing to overcome the drawbacks mentioned with reference to the prior art.
Such problem is solved by a process as above specified, characterised in that it comprises the following steps:
providing a plate member in a metallic material of relatively high hardness, provided with a plurality of points projecting from a surface thereof;
inducing, by compression of the plate member onto the flat member, the penetration of said points in the thickness of the flat member and the adhering of said surface of said plate member on a portion of the flat member at the bottom of the cooking vessel; and
stretching said flat member at least at said portion, causing the deformation and the clutching of said points inside said thickness.
The present invention further relates to a cooking vessel obtained according to the process as above defined, further comprising application steps of one or more non-stick layers, as well as finishing steps of the vessel.
The main advantage of the process for the manufacture according to the present invention lies in allowing an effective securing of the plate member without traumatising the materials and with no further specific steps required.
In fact, the manufacture of the cooking vessels can follow a normal manufacture process, comprising press-stamping and coining steps needed to securing the plate member, while the latter step can be carried out in parallel, yet in a substantially autonomous way.
Moreover, with the above described process it is possible to secure a plate member regardless of the latter extension with respect to those of the bottom portion at issue.